I ran my first marathon this month. It went well, and despite my fears, I had fun. I met my goals — qualified for the Boston Marathon with nearly half an hour to spare and came in second in my age group. But the big surprise was my coach’s advice the next day.

It will take four weeks to fully recover, he told me. That seemed like an awfully long time.

I was running again in three days, and I felt better than ever when I ran the week after. Who says recovery should take weeks?

As it turns out, there’s not much rigorous research on recovery after strenuous exercise. There have been almost no long-term studies, and there’s little agreement on what to measure or how to measure it. This aspect of competition is rife with unsubstantiated dogma.

One popular notion holds that however many miles you race, that’s how many days it takes to recover: A 10-mile race requires a 10-day recovery. Dr. Timothy Noakes, an exercise physiologist at the University of Cape Town in South Africa, dismisses that advice.

“The days-for-miles recovery theory was popularized in the 1970s but was not scientifically based,” he said.

Hirofumi Tanaka, an exercise physiologist at the University of Texas at Austin, said the question of recovery “is a tough one.”

“The answer will be dependent on what element of recovery you are interested in,” he said. “We do have some information about how long it takes to replenish muscle glycogen, the primary energy fuel during strenuous distance running. But we have no idea on other elements.”

Athletes who consume carbohydrates and, even better, some protein after an event can refill their muscles with glycogen within 24 hours. But this is short-term recovery, not at all what my coach was talking about.

Edward Coyle, a colleague of Dr. Tanaka, defines recovery in terms of sore muscles. In his studies, he has found it takes about a week for muscles to stop hurting and full strength to return, an estimate that pretty much describes what happened to me.

If your muscles are sore and you can’t exercise for several days or a week, you get a “detraining” effect, Dr. Coyle said. He did muscle biopsies of young men before and after a week of deliberate detraining — refraining from exercise — and examined the mitochondria, the tiny energy factories of the cells.

After a week of detraining, he found, it took the men three weeks to fully regain their running speed. If they detrained for a month, it took two months to regain their speed.

Muscle soreness is not so much of a problem for swimmers and cyclists, Dr. Coyle said, because those sports do not involve the leading cause of soreness: eccentric contractions during which a muscle lengthens, as happens when you run downhill. For cyclists, the main recovery issue is restoring muscle glycogen.

Some researchers have taken blood samples from athletes and looked at enzymes like creatine kinase that can indicate muscle damage or at proteins associated with inflammation. But Maria Urso, a research physiologist at the United States Army Research Institute of Environmental Medicine, said “All of these are highly variable between individuals and may not correlate with recovery.”

“As far as a specific measure for recovery, this is likely the world’s biggest mystery,” Dr. Urso said. “There are so many physiological changes that take place when you push a body to its limits, it would be impossible to make one measure and use it as a gold standard.”

Of course, there is one measure that ties everything together: performance. But it is not clear how to use that as a gauge of time to recovery.

“How can you judge recovery except by measuring performance in another exercise bout similar to the one that initiated the fatigue?” Dr. Noakes said. “Since we can’t ask people to run a marathon again, we never really know when full recovery has happened.”

So Dr. Noakes relies on the experience of great runners, who tell him that there is a large psychological component to recovery. Many elite marathoners run only one or two races a year. After a marathon, he said, it “probably takes at least six months for the mind to recover fully.”

It can take even more time to recover from longer races, in Dr. Noakes’s experience. He used to run the 90-kilometer (55-mile) Comrades Marathon in South Africa. He needed a year to 18 months before he was mentally ready to do it again.

But individuals vary. Dr. Urso once ran three marathons, taking just three months between each and spending three weeks recovering each time; she got faster with each race. Ryan Hall, one of the nation’s best marathon runners, set a United States record in the Boston Marathon last April, then ran another fast race in the Chicago Marathon in October. He raced again in the Olympic qualifying marathon in January and made the team.

Dr. Urso advises runners to spend two to three weeks after a marathon doing what she calls a reverse taper. Before a race, most athletes taper by gradually decreasing the intensity and duration of their workouts.

After a race, do it in reverse, she suggested: Gradually build up with runs that at first last no longer than 60 minutes.

“I would guarantee that most runners will be back to baseline performance within two to three weeks of the marathon if they follow a program such as that,” she said.

That’s what I’m doing. My coach, Tom Fleming, says this strategy is based on what he has learned working with me for four years and on his decades of experience. Being fully recovered means, to him, being mentally and physically ready to perform at your best.

“You have only run one marathon, and let’s be honest, you haven’t raced that much,” he told me. “I’d say I know you pretty darn well, and I’d say it will take four weeks for you to recover.”

I have signed up for a few races this spring: a 5-kilometer race, a 10-mile race and a half marathon. The first one is a full six weeks after my marathon. I guess I’ll never know if I really needed all four weeks for recovery.

A version of this article appears in print on 03/20/2012, on page D5 of the NewYork edition with the headline: Personal Best: Road to Race Recovery Is Littered With Variables.